Project 2 investigates the pathogenic mechanisms of CRS in collaboration with Project 1 (GHS) and Project 3 (UC) to test important hypotheses with clinical and potential therapeutic relevance in CRS. The four overarching hypotheses are: i) that nasal polyp (NP) tissue promotes activation, proliferation and differentiation of B lineage cells leading to their expansion and autoimmune antibody production in the NP; ii) that autoimmunity is responsible for recalcitrant disease in patients that require frequent surgical intervention; iii) that exacerbations of CRS are triggered by human rhinovirus (HRV), explaining their predominance during the respiratory virus season, and; iv) that infection of CRS patients with HRV activates B lineage cells in patients with CRS. We will test these hypotheses using laboratory investigations to understand observations made in humans and testing discoveries made in the laboratory in human subjects. To test the hypothesis that NP tissue supports B lineage cell expansion, we will assess proliferation in the B lineage cell populations within NP tissue. We will assess class switch recombination in NP using PCR based to detect AID and excision circles. We will use a tissue explant model to study the activation and expansion of B lineage cells. To test the association of autoimmunity with recalcitrant CRS disease, we will use a longitudinal study to determine whether autoimmunity is a predictor of recalcitrant disease. We will perform a cross sectional study with 150 patients from GHS to determine whether patients with a history of multiple surgeries have a greater prevalence of autoimmunity in the upper airways. We will determine whether HRV is an important cause of exacerbations of CRS two ways. First, we will collaborate with Project 1 to recruit 100 CRS patients undergoing an exacerbation. Microfluidic array analysis will identify the viral or bacterial pathogens associated with the exacerbation. We will also utilize experimental challenge of CRS and control subjects with HRV and test the hypothesis that HRV induces CRS exacerbations. We will monitor B lineage cells and epithelial cells from infected subjects will be subjected to microarray analysis in order to validate genes discovered in Project 3 to be important HRV and CRS associated genes.